Various kinds of coordinate measuring machines are known for precisely measuring a configuration of and dimensions of an object to be measured. Some of them consists of a base for supporting an object to be measured thereon, origin point blocks, each of which has a master ball serving as the origin of measurement and being disposed at a certain point on the base, a first moving device having a gantry shape and moving essentially horizontally on the base, a second moving device movable nearly horizontally on the first moving device, and a third moving device which vertically moves through the second moving device and is provided with a detector.
When detecting the dimensions and configuration of the object by the coordinate measuring machine, the detector is contacted with the master ball to set the origin for measurement, then touching the object by moving the first, the second, and the third moving devices respectively so as to measure the dimensions and configuration of the object.
It is known that such a conventional coordinate measuring machine is ordinarily operated in a special environmentally controlled room which is kept at an average temperature and humidity to enhance measuring accuracy. However, usually there are several production processes or steps required to produce commodities in a factory, so that if each process step requires the measurement of the dimension and configuration of the commodities, several conventional coordinate measuring devices will be needed in the factory. This causes some problems.
The temperature and humidity in a factory is not always constant and when processing the work by a machine tool, small grains of waste matter are raised, become suspended in the air and then become attached to the master ball.
In this case, because the coordinate measuring machine is expected to precisely measure the object, the dust particles on the master ball negatively influences the detector causing the detector to thereby miss the origin of measurement. Incidentally, a precise measurement of the object cannot be conducted.
An object of the present invention is to protect the origin point block from the dust suspended in the air and to prevent the dust from collecting on the master ball of the origin point block. Accordingly, the origin of measurement can be set precisely and the accuracy of measurement by the coordinate measuring machine is improved by the present invention.